Preface to Special Issue on Water Splitting,from Molecular toMaterial

Water splitting produces hydrogen (H2) as a green energy carrier, delivering new rooms for the usage of renewable but transient energy, such as solar and wind energy. The development is of fundamental significance to deal with environmental issues and to build carbon-neutral society. Oxygen evolution reaction (OER) in anode and hydrogen evolution reaction (HER) in cathode occur during the process. Both of these two half reactions involve the transfer of multiple electrons and protons and also the significant rearrangement of several atoms, leading to sluggish kinetics for these processes. Therefore, catalysts are required to accelerate these two reactions. Water-splitting catalysts can be divided into two branches, namely molecular and material catalysts. Molecular catalysts possess clear and systematically regulatable structures, which are favorable for mechanism and structure-function relationship investigations.